Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile have discovered a 26-light-year-long trail of heated molecular gas in the Large Magellanic Cloud, providing a smoking gun that links the binary star system LMC P3 to powerful microquasar jets rather than pulsar winds.
The stellar pair known as LMC P3 has stood out as a cosmic outlier. Located within our galactic neighborhood inside the dwarf satellite galaxy known as the Large Magellanic Cloud, it generates the most luminous gamma-ray emissions of any known binary star system. Unlike objects buried deep behind galactic core dust in the Milky Way, the Large Magellanic Cloud offers an unhindered view of complex astrophysical phenomena. The exact engine powering those high-energy gamma rays remained a persistent puzzle for researchers ever since the system’s discovery in 2016.
Following the Radio Trail through ALMA
Gamma rays sit at the highest energy limit of the electromagnetic spectrum, making direct tracing of their origin difficult. To solve the riddle, a research team led by scientists from Nagoya University and Gifu University turned away from gamma rays and focused instead on radio waves. Beginning in 2022, the team utilized ALMA bands 6 and 7 to examine DEM L241, the supernova remnant and cloud of cold molecular gas that surrounds the binary system. By measuring carbon monoxide emissions at wavelengths around 1.3 mm and 0.87 mm, the researchers mapped the structure, motion, and temperature of the surrounding material.
What they found changed the prevailing physics models.
The observations revealed a strikingly straight and narrow trail of molecular gas measuring approximately 26 light-years long and three light-years wide. While standard molecular gas in the region sits at a chilly 15 Kelvin, this newly mapped trail registers significantly hotter, between 35 and 60 Kelvin. This localized heating across a vast span of the cloud points directly to an energetic jet interacting with the surrounding material.
“We discovered a gigantic molecular jet.”
stated Yasuo Fukui, professor emeritus at Nagoya University and principal investigator of this fresh finding, which has been featured in The Astrophysical Journal Letters. Fukui noted that the relatively high temperature observed over a large fraction of the molecular cloud presents a compelling case that the gas is energized by a high-energy jet emanating from the system’s compact object.
| System Feature | Observed Measurement / Property |
|---|---|
| Host Remnant | DEM L241 Supernova Remnant |
| Binary Orbit Duration | Roughly 10 Days |
| Companion Star Mass | More than 30 times heavier than the Sun |
| Gas Trail Dimensions | 26 light-years long, 3 light-years wide |
| Heated Gas Temperature | 35 to 60 Kelvin (vs. 15 Kelvin ambient) |
Weighing Microquasars against Pulsar Winds
The discovery of the linear gas structure strengthens support for one of two competing theories regarding how gamma-ray binary emissions operate. Prior to the ALMA observations, many astrophysicists favored a pulsar wind mechanism. Under that framework, the compact object—a pulsar or a rapidly spinning neutron star—would emit a particle wind that collides with the stellar wind of its massive companion, creating shock waves capable of accelerating particles into gamma rays.
However, the newly identified jet signature points toward a different engine entirely.
The findings indicate a quasar-like mechanism operating on a stellar scale. In this microquasar scenario, the compact object—either a stellar-mass black hole or a neutron star—draws in material from its companion to form an accretion disk. That disk unleashes powerful jets of high-speed particles. Because black holes generally drive more robust jets than neutron stars, the exceptionally high gamma-ray output of LMC P3 strengthens the hypothesis that the central object is a black hole rather than a neutron star, according to the research team.
Bhuvana Gadikere Rajendra, a researcher, and Kisetsu Tsuge, a designated assistant professor—both affiliated with the Institute for Advanced Study at Gifu University—co-led the study alongside Hidetoshi Sano, an associate professor at the Graduate School of Natural Science and Technology at Gifu University. The research opens a clearer window into how compact objects shape their stellar environments long after the initial supernova explosion fades.
